This invention relates to a method for the reclamation of vulcanized rubber for the purpose of reuse, and more particularly to a method for producing highly useful reclaimed rubber on a commercial scale by highly efficient desulfurization of powdered scrap vulcanized rubber by the use of microwave energy. This invention, therefore, realizes improvement in the quality of reclaimed rubber.
As measures for attaining reuse of scrap vulcanized rubber, a method which finely pulverizes scrap vulcanized rubber and utilizes the resultant vulcanized rubber powder as a filler for unvulcanized rubber, a method which combines scrap vulcanized rubber with a regenerating agent and heats the resultant mixture so as to desulfurize and convert the mixture into reclaimed rubber, and a method which effects reclamation of rubber by a simple procedure of desulfurizing scrap vulcanized rubber at elevated temperatures through the agency of microwave, for example, have been heretofore known to the art.
When the scrap vulcanized rubber is finely pulverized to be used as a filler, however, the cost of the pulverization is high and the produced filler often finds only limited end uses. The method which effects reclamation by use of a regenerating agent entails a problem that the regenerating agent to be used therein goes to increasing the cost of reclamation and imparting to the reclaimed rubber pollutional, toxic, and odorous components. In the case of the method which provides simplified reclamation by the use of microwave, even after the desulfurization by heating is completed, the heat accumulated during the desulfurization causes the thermal decomposition of desulfurized rubber to proceed further and the consequent oxidation (exothermic reaction) of rubber molecules to induce fracture of main chains and thermal decomposition and carbonization of rubber and additional components. When the reclaimed rubber obtained by this method is blended with freshly supplied rubber, the pulverized rubber obtained from the resultant mixture suffers from heavy degradation of properties and often finds greatly restricted end uses.
There has been proposed, in Japanese Utility Model Application No. Sho 54(1979)-126761 (Unexamined Utility Model Publication Sho No. 56(1981)-44117) filed by the same applicant as the present patent application, a method for the vulcanization of reclaimed rubber as illustrated in the block diagram of FIG. 1.
This method, which comprises a step (a) for classifying scrap vulcanized rubbers by kind, a step (b) for pulverizing the separated vulcanized rubber into powder, a step (d) for desulfurizing the vulcanized rubber powder at elevated temperatures within a microwave heating chamber, etc., is characterized by interposing between the step (b) and the step (d) a step (c) for admixing the pulverized vulcanized rubber with a rubber process oil. Owing to the incorporation of the rubber process oil, the contact of rubber process oil, the contact of rubber molecules with oxygen is obstructed so much as to retard the aforementioned oxidation of rubber molecules. Even by this method, when the volume of scrap vulcanized rubber to be treated is large, the interior of rubber mass under treatment does not easily liberate heat thoroughly between the time the treatment is completed in the step (d) for microwave heating or a step (e) for secondary heating and the time the finishing treatment by rolling is started in a step (g) for finishing. Owing to the heat generated by the oxidation which is consequently suffered to proceed though gradually, the mass of rubber under treatment remains in an overheated state and, thus, tends to induce fracture of rubber molecules, decomposition of additional components (including rubber process oil), and carbonization of rubber and additional components. In this respect, the present method has not offered a perfect solution to the aforementioned problem. The step (e) for secondary heating is intended for improving the overall efficiency of heating by this method and is not always indispensable.